The invention relates to novel indole derivatives and a process for the preparation thereof.
Tryptophane is one of the essential amino acids and is widely utilized as medicine and food or feed additives.
There is known a process for the synthesis of tryptophane by reacting an .alpha.-isocyanoacetic acid ester with a quaternary salt of N,N-dimethylindolemethylamine (hereinbelow, referred to as gramine) to obtain an .alpha.-isocyano-.beta.-(3-indole)propionic acid derivative, and then hydrolyzing the derivative (see, Japanese Laid-open Patent Application No. 48-26758). This process is partly satisfactory but leaves the following points to be improved.
A. Many steps are required to obtain an .alpha.-isocyanoacetic acid ester from the starting material. In general, many steps are required to synthesize amino acids from simple starting materials. However, the commercial synthesis of amino acids should be attained by reduced steps. From this point of view, the above-mentioned process necessitates too many steps.
B. The above-mentioned .alpha.-isocyanoacetic acid ester is chemically unstable owing to the isocyano group and, therefore, the above-mentioned process which employs the ester as a starting material may often cause undesirable side reactions, which may cause a reduction in the yield. The process has a low processability and emits a foul odor.
C. By-products which are formed in the course of the conversion of the above-mentioned derivatives to amino acids cannot be reused. From the viewpoint of saving natural resources, it is desirable to be able to recycle the by-products to the process for the reuse thereof.
Therefore, it has been earnestly desired to develop a process for synthesizing tryptophane, in which only a few steps are required, the intermediate before the hydrolysis should be stable and a high yield should be obtainable and the by-products should be reusable.